Quality assurance is a wide-ranging concept covering all matters that individually or collectively influence the quality of a product. It is the totality of the arrangements made with the object of ensuring that pharmaceutical products are of the quality required for their intended use.
[Source: WHO. Good distribution practices (GDP) for pharmaceutical products]

QUALITY CONTROL

Quality control covers all measures taken, including the setting of specifications, sampling, testing and analytical clearance, to ensure that starting materials, intermediates, packaging materials and finished pharmaceutical products conform with established specifications for identity, strength, purity and other characteristics.
[Source: WHO. Good distribution practices (GDP) for pharmaceutical products]

QUALITY SYSTEM

An appropriate infrastructure, encompassing the organisational structure, procedures, processes and resources, and systematic actions necessary to ensure adequate confidence that a product (or services) will satisfy given requirements for quality.
[Source: WHO. Good distribution practices (GDP) for pharmaceutical products]

QUALITY-ADJUSTED LIFE YEARS (QALYS)

A measure of health outcome which looks at both length of life and quality of life.
QALYS are calculated by estimating the years of life remaining for a patient following a particular care pathway and weighting each year with a quality of life score (on a zero to one scale).
One QALY is equal to one year of life in perfect health, or two years at 50% health, and so on.
[Source: NICE Glossary]
See also: disability-adjusted life years